Crossed-field discharge device and microwave circuits incorporating the same



July 29, 1969 J. E. sTAATs 3,458,755

CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE CRCUIT INCORPORATING THE SAME l/ ATrYs. Y

July 29, 1969 J. E. sTAATs 3,458,755

CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE CIRCUITS INCORPORATING THE SAME Filed June 21, 1966 12 Sheets-Sheet 2 July 29, 1969 .1. E STAATS 3,458,755 CRossED-FIELn DISCHARGE DEVICE AND MICROWAVE cRcUITs INCORPORATING THE SAME Filed June 2l, 1966 12 Sheets-Sheet 3 3,458,755 CIRCUITS July 2'9, 1969 J. E. sTAATs CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE July 29, 1969 x. E. sTAATs CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE CIRCUITS INCORPORATING THE SAME Filed June 21, 1966 12 Sheets-Sheet 5 Fm. a

FIG.9

Julyv29, 1969 J. E. sTAATs y 3,458,755 CROSSED-FIELI) DISCHARGE DEVICE AND MICROWAVE CIRCUITS INCORPORATING THE SAME Filed June 2l, 1966 l2 Sheets-Sheet 6 UN/D/RECT/O ELECTRIC FIELD July 29, 1969 3,458,755

cRossED-F c v I c E A N D M1 AVE CIRCUITS IIIIIIIIIIIIIIIIII ME Filed June 21.

July 29, 1969 J. E. sTAATs 3,458,755

- CROSSEDFIELD DISCHARGE DEVICE AND MCROWAVE CIRCUITS IIIIIIIIIII NG THE SAME l2 Sheets Sheet 8 July 29, 1969 J. E. sTAATs 3,458,755

CROSSEDFIELD DISCHARGE DEVICE AND MICROWAVE CRCUITS IIIIIIIIIIIIIIIIII ME Filed June 21, 1966 l2 S eeee S-Sheet 9 COMPOSITE FIELDS July 29, 1969 J. E. sTAA-rs 3,458,755

CROSSED-FIELD DISCHARGE DEVICE AND MICROWAVE CIRCUITS INCORPORATING THE SAME Filed June 21, 1966 12 Sheets-Sheet 10 9/4 9,2 Fla lr 50 9'@ /.o e0 /.o /.o

800 ,WW m 82 I, Amperes July 29, 1969 J. E. sTAATs 3,458,755

CROSSEDFIELD DISCHARGE DEVICE AND MlCROWAVE CIRCUITS INCORORAT ING THE SAME 12 Sheets-Sheet 11 Filed June 21. 1966 July 29, 1969 .1. E. s'rAATs 3,458,755

cRossED-FIEDD DISCHARGE DEVICE AND MlcRowAvE cRcuITs INCORPORATING THB SAME Filed June 21. 1966 12 Sheets-Sheet 12 FIG. 20

TUNER A TTENUA ron OSC/LLATOR States ,Patent m@ 'cRossEDLFI'ELn Drscnlfmcu DEVICE ANn MICROWAVE CIRCILIITS lINCORPORATING "'THESAME" James E. Staats, Louisville,- Ky., assignor to General l? .Electric Company', acorporation of New York Filed June 21-1966,Ser.-No. 559,267

ABSTRACT ou THE DISCLOSURE' 'fThe're disclosedfa crossed-Infield discharge device including an annular sleevey surrounding a-pair of segmented and axially spaced-apart annular anode members and de- ,4

The present invention relates to an improved crossedfield discharge device, and to microwave circuits incorporating the same including microwave oscillator circuits and microwave amplifier circuits. f

It :is a general object of the invention to provide a new and improved Fcrossed-field discharge device 'for use atrnicrowave frequencies, whichfdevice is of exceedingly simple and economical construction and arrangement, and which device is particularly adapted for operation yupon the application of relatively low voltage operating potentials thereto.

,Another object of the invention is to provide an mprovedcrossed-field discharge device of the type set'forth which can provide an unusually high output of microwave energy in proportion tothe physical dimensions thereof, whereby to permit the miniaturization of -microwave circuits embodying the improved crossed-field discharge device of the present invention. p

lAnother objectof theinvention is to provide an improved crossed-field discharge device of thetype set forth comprising an annular anode structure defining therein an outer annular axially extending space enclosed thereby and y anfinnerv annular axiallyextending, space extending therethrough.and` a ,radially extending passage interconnectingthe 4outer `and linner axially extending spaces at longitudinal midsection ofthe anode structure, the radially extending passage dividing the anode structure into a first anotle,sectionA disposed adjacent to oneend thereof and Vazsecyond `anode section `disposed, adjacent tothe Iother endthereof,` agplurality Vof. axially extending ,anode seg- Inentso'nuthe innersurfacesofsaid anode sections and projecting radiallyintolhe inner axiallyextending space and providing a corresponding -plurality of axially extendinghanode .recessestherebetween, a plurality of axially @extending first .rodson'lthe first anode sectiondisposed respectively in th'eanoderecesses in the second anode section respectively spaced fromthe adjacent ones of the anode segments on the secondv anode, section, a plurality of axially extending second rods on the second anode section-respectively disposedin the` anode recesses in the )first-anode section and respectively spaced from adjacent ones vof the anode segments on thefirst anode section, an axially extending cathode'structure disposed in the inner axially extendingspace and A'cooperating withthe anode Patented July 29, 1969 sections to define an axially extending annular interaction space, the cathode structure including an electron emissive element disposed within the anode sections and adjacent to the inner portion of the interaction space, means for establishing a unidirectional magnetic field extending axially through the outer axially extending space and the interaction space, and end structures enclosing both the ends of the anode structure and the axially extending spaces, the anode structure including the axially extending spaces and the radially extending passageftherein defining a frequency determining folded resonant cavity for the device.

In connection with the foregoing object, it is another object of the invention to provide an improved crossedfield discharge device wherein the anode structure includes an annular sleeve and a pair of annular anode members disposed within the sleeve and a plurality of rods disposed adjacent to the inner surface of the anode members, the sleeve and the anode members being electrically connected at the opposite ends of the anode structure and the rods being electrically connected to the anode members at the other ends thereof, the sleeve and the anode members and the rods defining a frequency determining folded resonant cavity for the device of very small longitudinal extent.

Another object of the invention is to provide an improved crossed-field discharge device of the type set forth wherein the anode structure includes an annular sleeve and first and second annular anode members disposed in the sleeve, the portions of the anode members disposed toward each other having respectively first and second annular recesses on the outer periphery thereof to provide respectively first and second outer surfaces spaced inwardly with respect to the inner surface of the sleeve and to provide first and second annular end surfaces defining an outer axially extending space therebetween, the adjacent portions of the bodies being spaced apart axially to provide a lateral passage therebetween connecting the inner and outer axially extending spaces, the first and second anode members respectively having a plurality of axially extending anode segments on the inner surface thereof and projecting radially into the inner axially extending space and providing a corresponding plurality of axially extending first and second anode recesses respectively therebetween, and a plurality of axially extending first and second rods respectively on the first and second anode bodies disposed respectively in the second and first anode recesses and respectively spaced from the adjacent one of the second and first anode segments, thereby to define av frequency determining folded resonant cavity for the device.

In connection with the foregoing object, it is another object of the invention to provide an improved crossedfield discharge device of the type set forth wherein the inner surface of the sleeve and the first outer surface cooperate to provide an outer section of a first folded transmission line shorted at one end by the first end surface and connected at the other end through the lateral passage to the inner section of the first folded transmission line defined by the first anode segments and the second rods, the, inner surface of the sleeve and the second outer surfacecooperate to provide an outer section of a second folded transmission line shorted at one end by the second end surface and connected at the other end through the lateral passage to the inner section of the second transmission line defined by the second anode segments and the first rods, the frequency of the resonant cavity being equivalent to twice the combined length of the first and second folded transmission lines. y

Another object of the invention is to provide in a crossed-field discharge device of the type set forth an improved rod structure wherein the rods taper toward the outer ends thereof, thereby to provide improved thermal conductance, to provide lower circulating currents and vimproved circuit efficiency/,to improve mode stability and to reduce the phase shift of RF voltages at the ends of the rods thus to improve electron bunching and consequent improved electronic efficiency.

Another object of the invention is to provide an improved crossed-field discharge device of the type set forth wherein the anode structure provides short and low 1mpedance paths for rotating waves, thus improving mode separation and stability in the device when utilized as an oscillator. K

Another object of the invention is to provide an 1mproved crossed-field discharge device of the type set fort h wherein the anode structure comprises a sleeve and a pair of identical anode members having the anode segments and rods integral therewith, the anode members being producible by broaching operations to provide greater accuracy in the construction thereof, the anode members cooperating with the sleeve in a manner such as to permit complete assembly of the device prior to forming the hermetic seals therebetween.

Another object of the invention is to provide in a crossedfield discharge device of the type set forth an improved cathode structure including a plurality of circumferentially spaced electron emissive sections corresponding in number to the sum of the number of the first anode segments and the first rods, the emissive sections being shaped and located to minimize back heating of the cathode and to encourage emission of useful electrons and to discourage emission of non-useful electrons.

ln connection with the foregoing object, another object of the invention is to provide an improved crossedfield discharge device of the type set forth including inner and outer transmission line sections connected by a radially extending annular passage, the electron emissive sections being disposed closer to the anode structure at the outer ends thereof and being spaced farther away from the anode structure adjacent to the radial passage, whereby to minimize losses associated with fringed field distortion in the vicinity of the radial passage.

Another object of the invention is to provide an improved crossed-field discharge device of the type set forth wherein the cathode is utilized as a probe to extract RF energy from the device, the cathode structure being such that only two ceramic parts and two end seals are required.

Another object of the invention is to provide in an improved crossed-field discharge device of the type set forth, improved pole pieces at each end of the anode structure and hermetically sealed thereto and providing end plates i,

therefor, the pole pieces being shaped to provide the desired distribution of unidirectional magnetic fields through the axially extending spaces in the device, the pole pieces being shaped such that they can be stamped from a substantially flat sheet of material.

In connection with the foregoing object, it is another object of the invention to provide a crossed-field discharge device of the type set forth wherein the output connections are attached to the anode structure and the cathode structure respectively for withdrawing microwave energy from the device, the end spaces between the pole pieces and the anode members defining inductances of predetermined value providing for a predetermined coupling of the RF energy in the device to the output connections.

Another object of the invention is to provide an improved microwave oscillator incorporating therein a crossed-'field Vc'liscliaige device "of the"presnf'invention, the resonant circuit for thejoscillator being in the form of a folded resonant cavityl within the device.

A still further objectof the invention is to provide an improved microwave amplifier incorporatingvvtherein a crossed-field discharge device ofdthe present inyention.

A still further object of the invention is to provide an improved microwave circuit 4incorporating therein a crossed-field discharge device ofthe present invention together with means for modulating the output of the device, whereby to provide a' microwave oscillator having a modulated output and to provide a microwave amplifier having a modulatedoutput. i.

Further features of the invention pertain vto the particular arangement of parts of the crossed-Held discharge device and of the connection thereof in the vvarious microwave circuits, whereby the above-outlined and addif tional operating features thereof are attained. f

The invention, both as to its organization and method of operation, together with Vfurther objects and advantages thereof, will best be understoodby reference tothe followingl specification when taken in k'corniecltion with the accompanying drawings, in which: p I

FIGURE l is a schematic and'diagrammatic illustration of an oscillator circuit incorporating therein a crossed,- eld disccharge device of the present invention; i.

FIG, 2 is a View inverticanl section throughf the oscillator of FIG. 1 and illustrating the circiutco'nnections for the crossed-field dischargedevice including the magnetic field coils therefor and the coupler and filter construction used therewith; ,i l

FIG. 3 is an enlarged view in vertical section`through the crossed-field discharge device illustrated in the'oscillator of FIG. 2; i i I FIG. 4 is a partial horizontal section through the device of FIG. 3 along the line 4-4 thereof; i

FIG. 5 is a view in'horzontal section through the of FIG.'3 along the line 5-5 thereof;

FIG.` 6 is a fragmentary perspective view or portions of the two anode members illustrating themin a spaced apart posiiton; v

FIG. 7'is an end viewof one of the anode members forming .apart ofthe crossed-'field discharge device of FIG. 3;

in vertical sectionv through the anode device FIG. 8is a view member of FIG. 7along theline 8-8'thereof;

FIG. `9 Yis a partial diagrammatic lineal viewl as seen within the anode members; FIG. 10 is a view in horziontal'section'through the'device of FIG. 3 aiong the intero-#1o thereof;

FIGS.-4 11 to 16, inclusiveya'reistill furtherenlarged fragmentary views'in horizont'a'lsction throug'lithe device of FIG. 3 along theV line 11-'-1'1` thereof and illustrating the variouselectricalandmagnetic fields'therein'; FIGS. 17 and 18 are graphs plotting several operating characteristics of the crossed-field 'discharge device illusrratedinriossio io;v f' l' FIG. 19 is a vschematic and diagrami'natic illustration of an amplifier circuit for amplifying lthe output from the microwave oscillator of FIGZ, the' amplifier circuit "utilizing therein a crossed=eld discharge device'made inaccordance andembodying the principles'of the present invention; and f i 4 FIG. 2() is a view in vertical'sectionthrough Athe amplier circuit'of FIG. 19 and illustrating the'crosse'dlfield discharge device 'and the'ercuit connections therefor including theI magnetic field coils and the famplifier input circuits and output circuits. i f Referring 'to` FIG. 1k of the drawings, there isdiagrammatically illustrated an oscillator circuit 50 embodying the -features ofthe present invention, the oscillyator circuit'S havingibeen illustrated as connected to athree-wireEdison network of 236 volts, single-phase,v (S0-cycles AC, and including two ungrounded line conductors L1 and L2 anda grounded neutral conductor N, the three conductors mentioned being terminated at an associated electrical insulating block B. The circuit 50 also comprises a power supply 51 having a pair of input terminals 52 and 53 that are respectively connected to the conductors L1 and L2. A first pair of output terminals 54 and 55 is provided for supplying a rectied and filtered DC voltage of low amplitude for the purpose of applying the DC operating potential to the crossed-field discharge device of the oscillator circuit 50; and a second pair of output terminals 56 and 57 is provided for supplying a relatively low voltage AC power for the purpose of energizing the heater of the crossed-field discharge device of the oscillator circuit 50. More specifically, the input terminals 52 and 53 are connected to the output terminals 54 and 55 by a converter, the converter preferably being of the type disclosed in the copending application of James E. Staats, Ser. No. 181,144, filed Mar. 20, 1962, wherein there is disclosed a converter comprising an assembly of capacitors and rectifiers connected between the input terminals and the output terminals thereof, and characterized by the production of a DC output voltage across the output terminals thereof in response to the application of a low frequency AC input thereto across the input terminals thereof, whereby the amplitude of the DC output voltage from the converter is approximately twice the peak value of the AC voltage to the converter. The converter described is in fact a voltage doubler and rectifier circuit wherein the output DC potential therefrom at the terminals 54 and 55 is approximately 666 volts when the AC supply source has an R.M.S. voltage of 236 volts between the conductors L1 and L2, the 666 volts DC being the open circuit or no-load value for the DC output from the power supply 51.

The oscillator circuit 50 further comprises an oscillator 200 incorporating therein a crossed-field discharge device 100 made in accordance with and embodying the principles of the present invention, the oscillator 200 having a pair of input terminals 201 and 202 that are connected respectively to the DC output terminals 54 and 55 of the power supply 51 by means of conductors 60 and 61, respectively; the input terminal 202 is also connected by the conductor 61 to one of the low volta-ge AC output terminals 56 of the power supply 51. A third input terminal 203 is provided for the oscillator 200, the input terminal 203 being connected by a conductor 62 to the other low voltage AC output terminal 57 of the power supply 51. As illustrated, all of the parts of the oscillator 200 are surrounded by a metallic casing 205 to which is connected as at 206 an outer tubular conductor 207 within which is disposed an inner conductor 167 that is also connected to the input terminal 202, the coaxial conductors 167 and 207 providing an output connection for the oscillator 200. Connection is made to an output transmission line 65 including an outer tubular conductor 66 and an inner conductor 67 disposed therein, a rst capacitive coupling being provided by a coupler 232 between the outer conductor 207 and the outer conductor 66, and a second capacitive coupling being provided by the coupler 242 between the inner conductor 167 and the inner conductor 67. The capacitive coupling provided by the couplers 232 and 242 is desirable and necessary since for safety purposes the outer conductor 66 of the transmission line 65 must be grounded, which grounding of the outer conductor 66 is not possible if there is a DC connection to the oscillator casing 205, the casing 205 having a potential with respect to ground because of the application of operating potentials thereto from the voltage doubler and rectifier circuit 51, it being inherent in the construction and operation of the circuit 51 that neither the conductor 60 nor the conductor 61 can be grounded. Accordingly, it is also necessary and desirable that the power supply 51 and the oscillator 200 be electrically shielded by a grounded outer housing (not shown) disposed therebetween, all as is fully described in the aforementioned copending application Ser. No. 181,144.

The microwave energy supplied from the oscillator 200 to the transmission line 65 may be used for any desired purposes, two typical uses of the microwave energy being illustrated in FIG. l, the first use being illustrated in the upper righthand portion of FIG. 1 and the second use being illustrated in the lower portion of FIG. 1. Referring to the upper righthand portion of FIG. 1, in the first use of the microwave energy illustrated therein the transmission line 65 is coupled to an antenna of the type commonly used in search radar, the outer conductor 66 being connected to outer radiating or antenna elements 68 and the inner conductor 67 being connected to an inner radiating or antenna element4 69, the antenna elements 68 and 69 serving to match the impedance of the transmission line 65 to the impedance of the atmosphere. Referring to the lower portion of FIG. 1, in the second use of the microwave energy illustrated therein the transmission line 65 is coupled to an electronic heating apparatus, such as the electronic range 70 illustrated that is generally designed for home use. More particularly, the range 70 comprises an upstanding substantially box-like casing 71 formed of steel and housing therein a metal liner 72 defining a heating cavity therefor. The metal liner 72 may also be formed of steel, and essentially comprises a box-like structure provided with a top wall, a bottom wall, a rear wall and a pair of opposed side walls, whereby the liner 72 is provided with an upstanding front opening into the heating cavity defined therein, the casing 71 being provided with a front door 73 arranged in the front opening thus formed and cooperatin-g with the liner 72. More particularly, the front door 73 is mounted adjacent to the lower end thereof upon associated hinged structure 74, and is provided adjacent to the upper end thereof with a handle 75, whereby the front door 73 is movable between a substantially vertical closed position and a substantially horizontal open position with respect to the front opening provided in the liner 72. Also the front door 73 has an inner metal sheet that is formed of steel and cooperates with the liner 72 entirely to close the heating cavity when the front door 73 occuplies its closed position. For safety purposes, the inner liner 72 is connected by a conductor 76 to the outer casing 71 which is in turn grounded by the conductor N. The outer conductor `66 of the transmission line 75 is connected as at 78 to the casing 71 and to the liner 72 of the range 70, and there is provided within the range 70 at the rear thereof a radiating element or antenna 77 that is connected as at 79 to the inner conductor 67 of the transmission line 65. Accordingly, the microwave energy within the transmission line 65 is radiated into the cooking cavity of the range 70 to provide the power for cooking materials disposed therein. It further will be understood that in a preferred embodiment of the range 70, the power supply 50 and the oscillator 200 together with the transmission line 65 are all preferably disposed within a common housing that also includes the casing 71, the common housing fbeing preferably formed of metal, such as steel, and grounded for safety purposes.

Further details of the construction of the oscillator 200 and the crossed-field discharge device forming a part thereof will now be described with particular reference to FIGS. 2 to 10 of the drawings. The device 100 comprises an anode structure 101 including a sleeve 102 and a pair of anode members and 130, a cathode structure 150, a pair of opposed pole pieces 170, an upper end structure and a lower end structure 190.

The anode structure 101 is essentially annular in shape and is confined within the interior of the sleeve 102 (see FIGS. 3, 4 and 5), the sleeve 102 being generally tubular and having a circular cross section at all points therealong, the outer surface 103 thereof being cylindrical. The inner surface 104 of the sleeve 102 is also cylindrical in shape and has at each end thereof a recess to define an upper end wall 105 and a lower end wall 106, the end walls 105 and 106 being essentially annular in shape and disposed parallel to each other and normal to the axis of the device 100. Mounted on the sleeve 102 at essentially the midpoint thereof and extending outwardly therefrom is an exhaust tubulation 107 hermetically sealed thereto and communicating with the interior thereof, the exhaust tubulation 107 being useful to evacuate the device 100, the interior of the device 100 being evacuated to a'high degree and hermetically sealed as `will be explained more fully hereinafter. Also mounted on the outer surface 103 of the sleeve 102 is a stacked array of cooling fins 108, each of the cooling fins 108 being provided with an annular flange 109 that extends around the sleeve 102 and is lixedly secured thereto as by brazing. It will be understood that the sleeve 102 and the fins 108 are formed of a metal having good thermal conductivity, the preferred material being copper, thereby to accommodate conduction of heat from the device 100 outwardly therefrom and into the fins 108. The shape of the fins 108 is substantially rectangular so that they fit within the casing 205, there preferably being provided means for passing a cooling fluid, such as a stream of air, through the casing 205 and over the ns 108 to effect cooling thereof and a consequent removal of heat from the device 100 during the operation thereof.

Disposed `within the sleeve 102 and also forming a part of the anode structure 101 are the two anode members 110 and 130. Referring particularly to FIGS. 3 and 6 to 9, there is illustrated in detail the construction of the anode member 110. As illustrated, the anode member 110 is generally annular in shape and includes a body portion 111 disposed at one end thereof (the upper end as viewed in FIG. 3), the body portion 111 having an outer end wall 112 at one end thereof connecting with an annular outer wall 113 having an outer diameter only slightly less than the inner diameter of the sleeve 102, and specifically the inner surface 104 thereof, whereby the anode member 110 can fit within the sleeve 102 and ultimately is connected thereto as by brazing. The end of the body portion 111 opposite the end wall 112 is cut away or recessed to provide an annular inner wall 114 extending therearound and concentric with the annular outer wall 113 but having a substantially smaller diameter, the `walls 113 and 114 being joined by an annular end wall 115 disposed parallel to the outer end wall 112 and normal to the walls 113 and 114; the other end of the inner wall 114 connects with an inner end wall 116 that defines the other end of the body portion 111, the end wall 116 being disposed in a plane parallel to the end walls 112 and 115 and normal to the walls 113 and 114.

There is provided interiorly of the anode member 110 and extending the length of the body portion 111 a plurality of axially extending anode segments 117 that project radially inwardly into the axially extending space within the anode member 110 and providing therebetween a corresponding plurality of axially extending anode recesses 122, fifteen of the anode segments 117 and fifteen of the corresponding recesses 122 being provided in the anode member 110 as illustrated. Each of the anode segments 117 has an axially extending inner surface 118 and a pair of outwardly directed side walls 119 on the opposite sides thereof, the circumferential extent of the inner surface 118 being substantially less than the radial extent of the associated side walls 119. The outer ends of adjacent pairs of the side walls 119 are joined by an outer wall 121, whereby the recesses 122 are defined by the associated side walls 119 and the associated outer wall 121, the side walls 119 of each recess 122 converging inwardly and being disposed substantially normal to the associated outer wall 121.

The anode member 110 further has thereon and integral therewith fifteen rods or vanes 125, each of the ber and forms the inner surface of the associated rod 125. A portion of the side walls 119 on the anode segment 117 also extends forwardly beyond the inner end wall 116 to provide the radially extending sides of the associated rod 125, the inner sur-face 118 and the side walls 119 terminating at an end 126 disposed substantially normal to the axis of the anode member 11'0. An outer surface 127 is provided for each of the rods 125, the outer surface 127 extending from the inner end wall 116 inwardly to the rod end 126; more specifically, the inner end of the outer surface 127 joins the inner end wall 116 at a point spaced radially inwardly away from the adjacent outer walls 121 (see FIGS. 7 and 8) and tapers inwardly toward the associated inner surface from the end wall 116 to the rod end 126.

The anode member 130 is generally annular in shape and includes a body portion 131 disposed at one end thereof (the lower end as viewed in FIG. 3), the body portion 131 having an outer end wall 132 at one end thereof connecting with an annular outer wall 133 having an outer diameter only slightly lessithan the inner diameter of the sleeve 102, and specifically the inner surface 104 thereof, whereby the anode member 130 can fit within the sleeve 102 and ultimately is connected thereto as by brazing. The end of the body portion 131 opposite the end wall 132 is cut away or recessed to provide an annular inner wall 134 extending therearound and concentric with the annular outer wall 133 but having a substantially smaller diameter, the walls 133 and 134 being joined by an annular end wall 135 disposed parallel to theA outer end wall 132 and normal to the walls 133 and 134; the other end of the inner wall 134 connects with an inner end wall 136 that defines the other end of the body portion 131, the end wall 136 being disposed in a plane parallel to the end walls 132 and 135 and normal to the walls 133 and 134.

There is provided interiorly of the anode member 130 and extending the length Of the body portion 131 a plurality of axially extending anode segments 137 that project radially inwardly into the axially extending space within the anode member 130 and providing therebetween a corresponding plurality of axially extending anode recesses 142, fifteen of the anode segments 137 and tif-teen of the corresponding recesses 142 being provided in the anode member 130. Each of the anode segments 137 has an axially extending `inner surface 138 and a pair of outwardly directed side walls 139 on the opposite sides thereof, the circumferential extent of the inner surface 138 being substantially less than the radial extent of the associated side walls 139. The outer ends of the side walls 139 are joined by an outer wall 141, whereby the recesses 142 are defined by the associated side walls 139 and the associated outer wall 141, the side walls 139 of each recess 142 coverging inwardy and being disposed substantially normal -to the associated outer wall 141.

The anode member 130 further has thereon and integral therewith fifteen rods or vanes 145, each of the rods 145 being integral with and extending longitudinally from one of the anode segments 137. More specifically, the inner surface 138 of each of the anode segments 137 ex-tends forwardly beyond the inner end wall 136 and substantially parallel to the axis of the anode member 130 and forms the inner surface of the associated rod 145. A portion of the side walls 139 on the anode segment 137 also extends forwardly beyond the inner end wall 136 to provide the radially extending sides of the associated rod 145, the inner surface 138 and the side walls 139 terminating at an end 146 disposed substantially normal to the axis of the anode mem-ber 130. An outer surface 147 is provided for each of the rods 145, the outer surface 147 extending from the inner end wall 136 inwardly to the rod end 146; more specifically, ythe inner end of the outer surface 147 joins the inner end wall 136 at a point spaced radially inwardly away from the adjacent outer wall 141A and tapers inwardlyvtoward the associated-inner surface from the end wall 136 to the'rod end 146. i f vThe anode members 110 and.,130`are also formedof a metal-havingl good thermal conductivity, the'l preferred material being' copper. The 'sleeve `-102 'and the anode members 110 and 130 also must 'haveV good electrical conductivity, the Icopper providing-the necessary.. good electrical conductivity as well as the good-thermalconductivity. The geometry of the anodemembers 110 and 130 is such that the-exterior surfaces-112, 113, 114, 115, 116, 126 and.127 on `the anode member 110 and the surfaces 132, v133, 134,135,` 136, 146'. and 147 on `the anode member'130 canr all. be formed by machining a block of copper;.and all of the interior surfaces of the anode lmembers 110 and 130 including the surfaces 118, 119, 121, 138, 139 and 141 canall be formed by broaching, -wherebytheanode member v110 and 130 canfbe formed integral from blocks of copper, thus toprovide greater accuracyof the parts than is possible by joining such as by brazing, individual segments of the anode members 110 and 130. As illustratediin FIG. 3the anode member 110V is disposed in the upper portionof the sleeve 102 with the -body portion 111 thereofl disposed upwardly and with the rods -125 thereof extending downwardly; the anode member 130 is disposed in the lower portion of the sleeve 102 with the body` portion 131 thereof-disposed downwardly and with the rods 145 thereof extending upwardly. As is also illustrated in FIGS. 6 and 9, the anode members 110 and 130 are rotated slightly with respect to each other so that thee anode rods 125 on the anode member 120 are disposed inthe centers of the recesses 142 of the anode mem-ber 130, and conversely the anode .rods 145 on the anode member.130 are disposed in the `centers of the recesses 1,22 of the anode member 110. In this arrangement, there is one of the anode rods v125 disposed in each of the anode recesses 142 and equidistantly `spaced from the adjacent anode segments 137, and likewise there is one of the anode rods 145.dis posed in each of the anode recesses 122 and equidistantly spaced from the adjacent anode segments 117, all as is diagrammatically illustrated in FIGS. 5, 6 and 9.

The sleeve 102 and the anode members 110` and 130 also cooperate to provide an outer axially extending space 1 20, the space 120 being annular in shape `and bounded on the outer portion by the inner wall 104 of the sleeve 102 and on the inner portion bythe inner walls 114 and 134 and at the upper and lower ends by the end walls 115 and 135. The interior of the anode members 110 and 130 form a secondl or inner axially extending space within whichV is disposed the cathode structure 150, the space between the outer surface of the cathode v structure 150 and the facing surfaces 118 and I138v defining an annular axially extending interaction space 1,60. Furthermore, the inner end walls 116 and 136 are spaced apart to provide therebetween a raidallyextending `annular passage 140 interconnecting the outer space 120y va'tthe mid-portion thereof to the inner axially extending space at the imidportion thereof and tothe interaction'space 160 atuthe mid-portion thereof.

The cathode structure 150 is "provided in the" axially extending spacedened bygthe lanode mem-bers 110 and 130, the Acathode structure 150" including a 'cylindrical metal wall 151V (see FIGS. 3 and 5) arrange d with v'the axis thereof disposed at the 'axis of thedevice 100, the wall 151 being formed of a heat resistant and electrically conducting metal, the preferred material of construction beingk nickel. Mounted on'each end of the wall A151 is a cathode end 152, the cathode? ends 152' beingA substantially identical in construction', whereby' the same reference numerals have beenapplied Itolike parts of both. Referring to the upper cathode end l152, it includes' a substantially ilat rvannularcenter plate 153 vcarrying on the outer edge thereof an axially'directed annular inner tlange 154 Vcarrying on the inner.. e n d`v thereofl angoutwardly directed dat llange 155; the outer :periphery of theilange 155 carries a mounting llange. 156 thereon' extending outwardly and disposed within the adjacent end 'of the wall 151 and suitably secured thereto as by welding. The outer edge of the flange 156 carries aradially and outwardly extending shield flange 157 thatextends radially outwardly beyond the wall 4151l and overlies the adjacent end of the interaction space 160. Each center plate 153 has a central opening 158 therein, thelower cathode end 152 carrying on the inner edge and surrounding the opening 158 therein a center end tlange 159. The cathode ends 152 are also-preferably vformed ofv nickel. The upper cathode end 152 is .mechanically ,and electrically connected to a cathode stud-167, the cathode stud 167 being generally circular in cross section and having at the lower end thereof a reduced diameter portion 168 that extends through the opening'158 in the cathode end 152 and is xedly secured thereto as by a pair of outwardly directed flanges 169. It will be appreciated that'the upper end of the cathode structure 150 is both electrically and mechanically connected to the stud 167. Y

The cathode wall 151 is provided with a sintered porous coating 161'impregnated with a suitable electron emissive oxide material, whereby upon heating of the cathode structure 150, the coating 161 readily emits electrons from the outer surface thereof. Referring particularly to FIG. 5, it will be seen that the coating 161 is shaped to provide a plurality of outwardly extending projections 162 each having outwardly converging side walls joining a generally circumferentially arranged outer surface 163, a space 164 being provided between the adjacent projections 162. As illustrated, the circumferential extent of the outer surface 163 is substantially equal to the space 164 between the adjacent projections 162. The preferred range of the circumferential extent of each of the outer surface 163 is approximately 25% to approximately 60% of the circumferential distance ybetween the centers of adjacent outer surfaces 163. The number of projections 162 provided on the coating 161 is equal to the sum of the number of the anode segments 117 and the num-ber of cooperating rods 145, for example, and is likewise equal to the sum of the number of the anode segments 137 and the number of the cooperating rods 125, whereby there are thirty of the projections 162 provided upon the coating 161. The outer surfaces of the coating 161 together with the inner surfaces 118 and 138 on the anode members and 130, respectively, dene the interaction space 160 disposed therebetween in which the emitted electrons from the coating 161 interact with the electrical elds and the magnetic fields disposed between the anode structure 101 and the cathode structurev-150. As will be described more fully hereinafter, the projections 162 combine withy the anode segments 1 17 and 137 and, with the rods and 145 to provide la preferred distribution of the several .elds within the interaction space 160 of the device 100 that results in more desirableoperating characteristics thereof. One particularly desirable result of the shape of the coating 161 is lthe minimized 'back heating of the cathode structure 150, the ldesirable emitted electrons emanating from the projections 162, and the undesirable emitted electrons emanating from the space 164 between .the projections 162, thereby to facilitate the emission of desirable electrons and to-suppress the emission ofV undesirable electrons.. v l

Itfurther will be noted from FIG. 5 that the center line of each projection 162 is v circumferentially displaced relative tothecenter line of its .corresponding anode segment 117 and 137 or. its correspondingrod 125 and 145, as the case 'may be; more 4specificallyQthe center line of the projections 162 are displaced in a clockwise direction a circumferential ydistanceetglual to approximately 40% of the circumferential spacing between thecenter lines of an adjacent anode segment 117 and an adjacent rod (for example 5f rotation for a 12f spacing or a percentage of 41.8%Y as illustrated). The circumferential displacement of ythe projections 162 withrespect to the corresponding anode segments orjrods is preferably in the range -between and approxiamtely 45% of the circumferential spacing between adjacent anode segments and rods, the preferred range being between approximately 25% and 45% of the spacing between adjacent anode segments and rods, a still more preferred range be-V ing between approximately 35% and 45% of the spacing between adjacent anode segments and rods. Furthermore, the displacement is on the downstream side, i.e., in the direction of normal initial electron ow from the projections 162. It also will be noted that the electron emissive coating 161 is confined between the outer .end walls 112 and 132 of the anode membersll and 130, respectively, the cathode structure 150 being carefully centered with respect to the anode members 110 andy 130, whereby each of the cathode projections 162 extends axially of the device 100 parallel to the axis thereof and confined -between the outer end walls 112 and 132.

The radial dimension of each of the projections 162 varies from end to end of the cathode structure 150. Adjacent lto the outerends of the cathode structure 150, the radial dimensions of each of the projections 162 is preferably greater than about 20% of the spacing between the anode surfaces 118 and 138 and the coating 161 on the cathode structure 150. At the longitudinal midpoint of the emissive coating 161, an area 166 of reduced radial dimension is provided, the radial extent of the projections 162 being substantially nil and in certain instances the coating 161 being completely removed at the center reduced portion 166; the portion 166 is opposite the annular passage 140 betweenthe anode members 110 and 130. There further is provided an intermediate reduced portion 165 between the center reduced portion 166 and each of the outer ends of the cathode structure 150, the intermediate reduced portions 165 having roughly one-half of the radial extent of the projections 162 that are found at the outer ends of the coating 161. The longitudinal extent of the outer coating portions are substantially equal to the longitudinal extent'of the intermediate reduced portions 165, which are in turn substantially equal to the longitudinal extent of the center reduced portion 166. In a typical construction of the coating 161, the difference in the thickness of the coating is approximately mils from one section to the adjacent section of the coating 161.

The stepped construction of the coating 161,v i.e., the provision of the reduced portions 165 and 166, serves to match the electronic impedance of the interaction space 160 to the RF `load impedance coupled to the' output of the device 100 in a manner that improves the eiciency and load range of the device 100. More specifically, it has been found that the load impedance transferred to the `in teraction space 160 varies axially therealong, the load impedance being low adjacent to the outer ends of the interaction space 160 and increasing to a maximum at the longitudinal midpoint thereof. For a given combination of operating voltage, magnetic field and current through the device 100, there is a single value of'RF output voltage and load impedance which produces a maximum efiiciency of operation,whereby if the loadimpedance varies axially of thedevice 100, there is-only one point axially ofthe interaction space 160 which produces the 'maximum operatilng eiciency. In accordance with the present invention, the plurality of vcathode sections of varying diameterare arranged such that the anode to cathode spacing varies in a mannerso that the electronic impedance of each section of the interaction space 160 matchesthe RF load impedance at each section of theinteraction space. As a result, the efciency of the deviceV 100 with a cathode of constant cross section from end to end thereof may be for example 40%; by incorporating the stepped cathode 150 of the present invention in the device 100, the eieiency of operationv can be improved to 45 and up to 50% under optimum conditions.

As illustrated, the cathode structure 150 is ofthe indirectly `heated type, and accordingly, there'has been provided within the cathode wall 151 a heater 176 in the form of a coiled filament extending substantially the entire length of the cathode wall 151 and spaced inwardly a short distance `from the inner surface thereof. The upper end of the heater 176 as viewed in FIG. 3 has an outer end or terminal 177 that extends outwardly into an opening in the lower end of thev cathode stud 167, and specifically through an annular opening in the reduced portion 168 thereof and is mechanically and electrically connected to the cathode stud `167 whereby the cathode structure 150 and the heater 176 are both mechanically and electrically connected to the cathode stud 167. The lower end of the heater 176 has an outer end or terminal 178 that extends into an opening in the upper/end of a conductor 197 and is mechanically and electrically secured thereto. The conductor 197 is preferably formed of copper and extends outwardly and into a threaded connector 196. It will be noted that the heater terminal 178 is spaced from and electrically insulated with respect to the lower end of the cathode structure 150. Y

"Mountedwithin the outer ends of the anode sleeve 102 and forming end walls for the device are the pole pieces 170, the pole pieces 170 being identical in construction, whereby the same reference numerals have been applied to like parts of both of the pole pieces 170. The pole pieces 170 are formed of a material having high magnetic permeability, the perfcrred material being a low carbon steel, and are copper plated to render the outersurfaces thereof highly conductive to RF energy. As illustrated, each ofthe pole pieces 170 is generally cylindrical in shape including'a first substantially at innerI plate 171 disposed centrally thereof and disposed in a plane substantially normal to the longitudinal axis of the device 100 and in longitudinal alignment with the interaction space 160. Disposed about the periphery of the inner plate 171 and integral therewith is an annular coupling lian-ge 172 extending outwardly therefrom and carryingon the outer edge thereof an outwardly directed outer plate 173 that is substantially flat and lying in a plane normal to the axis of the device 100 and being in longitudinal alignment with the adjacent end of the outer axially extending space 120. The outer edge of the outer plate 173 carries an annular and outwardly extending mounting flange 174 that has 'an outer diameter slightly less than the inner diameter of the associated recessed end of the anode 'sleeve l102' to be received therein and hermetically sealed thereto. Finally, 4there is provided centrally of each 'of the inner plates 171 a circular opening 1175 in general longitudinal alignment with the adjacent end of the cathode structure 150, and specifically the adjacent Cend V of the 'cathode wall 151, the opening 175 receiving the'terminals of the cathode structure and heater therethrough." Preferably the pole pieces 170 are each formed of as ingle sheet of low v*carbon steel shaped as described by a stampingoperation, thereby to provide accurate dirriensions,therefor together with an inexpensive manufacture thereof.`

lAvn lupper en d structure 1 80 is provided at the upper end of the device 100 as viewed in FIG. 3 and a lower end structure 19t) isiprovided at the lower end of the device 1,00, the end structures 180 and'190 serving to provide a hermetic seal between the associated pole pieces 170 and the associated connections to the cathode structure 150 and/or theheater 17.6, as the case may be. The flipper end structure 180'includes a short tube 181 having the lower endj thereof disposed within the opening inthe upper pole piece'170 and suitably hermetically secured thereto as by brazing and extending upwardly therefrom substantially concentricuwith the longitudinal axis of the device 100 and the axis of the cathode stud 167. The upper end of the tube`181 receives therein the lower end of an annular insulator 182 which is formed, for example, of a good electrically insulating ceramic, the tubeY 181 being hermetically sealed to the insulator 182.

There is provided about the cathode stud 167 at the portion thereof adjacent to the reduced portion 168 a ring 183 that lits within a recess in the lower end of the insulator 182. Surrounding the upper end of the insulator 182 and the adjacent portion of the cathode stud 167 is a cap 185, the cap 185 being generally annular in shape and including an annular flange 186 surrounding an Outer periphery of the upper end of the insulator 182 and being hermetically sealed thereto. Integral with the upper edge of the outer ange 186 is an inwardly directed flange 187 carrying on the inner edge thereof an outwardly directed annular inner ilange 188 surrounding the adjacent portion of the stud 167 and hermetically sealed thereto as by brazing. It is pointed out that the sleeve 181 and the cap 185 are both formed of a material that can ybe readily secured both to a metal surface and to a ceramic surface, the preferred material being Fernico alloy, a typical composition being 54% iron, 28% nickel and 18% cobalt. lt will be seen that the upper end structure 180 forms a good hermetic seal that also provides electrical insulation between the upper pole piece 170 and the output conductor in the form of the cathode stud 167, the end structure 180 likewise providing the necessary mechanical support of the cathode structure 150 to position it within the anode structure 101.

In the lower end structure 190, a ceramic insulator 191 is provided that is annular in shape and has an outer diameter just slightly less than the diameter of the opening 175 in the lower pole piece 170 and an inner diameter just slightly greater than the external diameter of the centering flange 159 on the lower cathode end 152, whereby the insulator 191 serves to center the lower end of the cathode structure 150 with respect to the lower pole piece 17 0. The insulator 191 extends outwardly well beyond the lower pole piece 170 and there is provided a seal member 192 annular in shape and surrounding the insulator 191, the seal member 192 including a mounting flange 193 flxedly secured as by brazing to the outer surface of the inner plate 171 on the lower pole piece 170, the mounting flange 193 having integral therewith an annular wall 194 carrying an outer flange 195 that is inwardly directed and surrounds and is secured to the outer wall of the insulator 191. The seal member 192 is made of the same material as the sleeve 181 and the cap 185 and is hermetically sealed both to the lower pole piece 170 and the insulator 191. The outer end of the insulator 191 carries thereon a second seal member 198 that overlies the outer end thereof and is suitably secured as by brazing to the connector 196, the seal member 198 including an annular ange 199 surrounding the outer end of the insulator 191 and sealed thereto. The seal member 198 is formed of the same material as the seal member 192 and is hermetically sealed both to the insulator 191 and the connector 196. The lower end structure 190 therefore serves hermetically to seal the lower end of the device 100 and also provides electrical insulation between the lower end of the cathode structure 150 and the associated pole piece 170 and the heater 176, all while providing for the mechanical support of the lower end of the cathode structure 150 and the lower end of the heater 176.

When the device 100 is incorporated as a crossed-field discharge device in a microwave circuit, the pole pieces 170 arranged adjacent to the opposite ends of the anode structure 101 are utilized for establishing a unidirectional magnetic field extending axially through the several spaces within the anode structure 101, and specilically through the axially extending space 120 and through the interaction space 160, as well as the annular passage 140 and the various spaces between the anode members 110 and 130. To this end a pair of magnet coils 210 and 215 has been provided, the magnet 'coil 210 being disposed about the upper end of the device as viewed in FIG.`2 and the magnet coil 215 being disposed about the lower end of the device 100 as viewed in FIG. 2. The magnet coils 210 and 215 are both shaped -asa ,torous, ,are woundA of electrically conductive wire, and as illustrated, are disposed respectively about magnet yokes `211'1and-216,respec tively, that are each `in the form of aicylinderfdisposed within the opening 4in the vassociatedvrna'gnet coil. -There further are providedl outwardly :extendingvganges 212 and 217, respectively, about ythe outer ends of-thermagnet yokes 211 and'216 and secured respectively -thereto,.the casing 205 being disposed withinthe flanges :212 and 217 and forming both a mechanical connection-and a good magnetic path therebetween. -ilt .will beunderstood that the pole pieces 170, the magnet yokes 211-andf216, the flanges 212 and 217 and the casing 205 are all vformed Yof metals having a high magnetic permeability, suchas soft iron and low carbon steel,- whereby when the magnet coils 210 and 215 are energized,lastrong-and uniform unidirectional magnetic eld ris established between the pole pieces 170 within the device 100 and extending -axlally through the spaces within the device and specifically extending axially through the outer axially extending space and the interactionspace 1160 therein The circuit for energizing the coils 210 and 215 can be traced with reference to FIGS. l and 2 from the power supply 51, and specifically the DC output terminal 54 thereof, through the conductor 60 to the input terminal 201 of the oscillator 200 to which is connected one terminal of the upper magnet coil 210. The other terminal of the 4upper magnet coil 210 is connected by a conductor 213 to one terminal of the lower magnet coil 215, and the other terminal of the lower magnet coil 215 is connected by a conductor 218 to one of the cooling ins 108 by means of a connection 219, whereby the input terminal 201 is connected via the upper magnet coil 116, the conductor 213, the lower magnet coil 215, the conductor 218 and the cooling l'ln 108 to the anode sleeve 102` of the device 100. The flow of current through the magnet coils 210 and 215 serves to produce the unidirectional magnetic field in the various spaces of the device 100 and specifically in the outer space 120 and the interaction space 160 thereof.

Referring now to FIG. 2 of the drawings, the manner in which the crossed-field discharge device 100 is incorporated in the oscillator 200 will be described in further detail. The tubular conductor 207 is provided formed of a material that is electrically conductive, the conductor 207 having the lower end thereof received within the upper pole piece coupling ange 172 in telescoping relation therewith and is electrically connected thereto, the conductor 207 also being disposed within theupper magnet yoke 211 and extending` upwardly and beyond the upper end thereof. As is illustrated in both FIGS. 2-and 3, the cathode stud 167 at the upper'end of the crossedeld discharge device 110 has'the outer end thereof disposed below the outer end of the associated magnet yoke 211. The cathode stud 167 and the conductor 207 form a coaxial transmission line v.that provides output RF terminals for the oscillator 200, the terminals having applied therebetween the output RF energy. from'the oscillator 200. In addition, the outer conductor 207 has applied thereto the B+ potential from the conductor 60 which is connected thereto' via the input terminal' 201, the '-upper magnet coil 210, the conductor213, the lower magnet coil 215, the conductor 218the cooling iin ,108 to which is made the connection 219, :fthe anode ysleeve 102 and the upperpole piece 170, the upper pole piece 170,being directly connected to the,lower=end=ofthe `outer conductor 207as illustrated;Accordingly, v'it'zwill Ybe seen that the kouter conductor 207= not only serves as one: of the RF terminals for the devicef100 but also is'in direct electrical connection with the B+ `potential on the anode sleeve 102. Likewise, .the cathode lst ud 16T-not onlylhas the RF output energy `thereon `but has applied thereto both the Bf potential for the cathode ofthe ydevice 100 and the low voltage AC potential Vfor `energizing the heater 176. .:L l

f In order to accommodate the application to and the presence of the various potentials named on the output terminals 167 and 207 while preventing the introduction of RF energy into the power supply 51, and while preventing the application of the B+ and B- potentials to the output transmission line65, there has been provided a coupler and filter structure 230. Referring to FIG. 2, it will be seen that the coupler and filter structure 230 includes arfirst RF output terminal in the form of an annular outer conductor 231 which is capacitvely coupled to the conductor 207 by a coupler 232, the coupler 232 including a sleeve 233 of electrically insulating dielectric material, the sleeve 233 preferably Vbeing formed of a synthetic organic plastic resin, the preferred resin being a tetrafluoroethylene resin sold under the trademark Teon. The insulating sleeve 233 is disposed around and firmly embraces the outermost end of the tubular conductor 207 and extends upwardly therebeyond; the lower end of the outer conductor 231 is in turn placed in telescoping relationship about the sleeve 233, the lower end of the conductor 231 telescopically overlapping the upper end of the conductor 207 for a distance equal to A of the wavelength of the frequency of operation of the oscillator 200 in order to provide a portion of a second harmonic filter as will be described more fully hereinafter.

` An openingis provided in the side wall of the conductor 207 adjacent to the upper end of the oscillator 200, and joining the conductor 207 and surrounding the opening in the side wall thereof is a second annular conductor 234 that is suitably secured as by welding to the conductor 207 and extends laterally therefrom and to the right as viewed in FIG. 2 with the longitudinal axes of the conductors 207 and 234 disposed substantially normal to each other. Disposed in the conductor 207 adjacent to the junction thereof with the conductor 234 is a pair of annular insulators 235 and 236 substantially filling the conductor 207 and spaced apart a short distance from each other, the insulators 235 and 236 being formed of an electrically insulating dielectric material, the preferred material being a synthetic organic plastic resin, the preferred resin being a tetrafluoroethylene resin sold under the trademark Teom The lower insulator 235 has an opening centrally therein that receives therethrough a portion of a bullet 237 having on the lower end thereof a plurality of spring fingers 237a that resiliently grip the upper end of the cathode stud 167 to form a good electrical contact and mechanical interconnection therewith, a laterally extending flange 237b extending around the `bullet 237 and being disposed below and in supporting relationship with the insulator 235.

Extending upwardly through an opening in the center of the bullet 237 is a probe 238 in the form of a solid rod of electrically conductive material, the preferred material `being copper. The probe 238 passes through an openingin the center of the insulator 236 and upwardly therebeyond, the insulator 236` having an upstanding flange 23611 surrounding the probe 238. A suitable fastener such as a screw 239 is provided at the lower end of the probe 238 and threadedly engages a complementarily threaded opening at the lower end thereof, the head of the screw 239 overlying the lowersurface of the bullet 237. Arranged about and in telescoping relationship with the upper end of the probe 238 is an annular inner conductor 240 that has the lower end resting upon the insulator 236 and, surrounding the upstanding flange 23611 thereon, the upper end of the conductor 240 having an enlarged section 240a thereon that extendsv upwardly well beyond the probe 238 and `telescopically receives therein a second tubular inner conductor 241 that serves as an RF output terminal for the coupler and filter structure 230, whereby the conductors 231 and 241 provide the RF output terminal for the coupler and filter structure 230, whereby the conductors 231 and 241 provide the RF output terminals for the coupler and filter structure 230. A

capacitive coupling is provided between the probe 238 and the conductors 240 .and 2.41 by a coupler 242 including an annular washer 243formed of an electrically insulating dielectric material, the preferred material being a synthetic organic plastic resin, the preferred resin being a tetrafluoroethylene resin sold under the trademark Teflon The washer 243 surrounds the upper end of the probe 238 and is seated in the enlarged portion 240g at the upper end of the conductor 240 and serves fixedly to position the upper end ofthe probe 238 with respect to the conductors 240 and 241. A second fastener in the form of a screw 239 is provided in the upper end of the probe 238 and-has a threaded shank threadedly engaged in a complementarily shaped threaded opening in the upper end of the probe 238, the head of the screw 239 engaging the upper surface of the insulating washer 243, whereby the two opposed screws 239 serve fixedly to interlock the insulators 235 and 236, the bullet 237, the conductor 240 and the insulating washer 243.

The B- potential. and the low voltage AC filament supply for the device are connected to the probe 238 and thus to the device 100 through connections in the conductor 234, and specifically through a conductor 244 disposed within and concentric with-the outer conductor 234. The conductor 244 carries on the lefthand end thereof as viewed in FIG. 2 a connector 244a having an opening therein that receives therethrough the probe 238, whereby to make good electrical connection therewith. Disposed about the conductor 244, and between the outer conductor 234 and the inner conductor 244 is an annular insulator 245 formed of an electrically insulating dielectric material, the preferred material being a synthetic organic plastic resin, the preferred resin being a tetrafluoroethylene resin sold under the trademark Teflon Disposed to the left of the insulator 245 is an enlargement or ange 244i; on the conductor 244, and disposed to the right of the insulator 245 is a cylindrical choke 246 in the form of a tubular conductor that surrounds and receives therethrough the conductor 244 arranged concentrically therewith, the insulator 245 having a laterally extending flange 245a surrounding the conductor 244 and extending into the lefthand end of the choke-246 to position the adjacent end of the choke 246 with respect to the conductor 244. A conductive nut 247 is provided about the conductor 244 adjacent to the righthand end thereof and including a flange 247a extending into the righthand end of the choke 246 to position the adjacent ends of the conductor 244 and the choke 246 with respect to each other. The righthand end of the conductor 244 isthreaded as at 244e` and threadedly engages an internally threaded opening in the nut 247 to lock the insulator 2 45 and the choke 246 against the ange 244b; the threaded end 244C is connected to the input terminal 202 formed of a conductive metal, the terminal 202 having an enlarged lefthand end 249 having a threaded opening therein to receive the adjacent threaded end 244e Vof the conductor 244. The terminal 202 extends outwardly to the right beyond the outer conductor 234 and is connected to the conductor 61 from the power supply'51. Connected between the outer conductor 234 and the inner terminal 202 is a filter capacitor 248 of the feed through type that is in the form of two layers of conductive foil between which areA interposed layers` of insulating film, thelayers of conductive foil and insulating film being wound to form the capacitor 248, one terminal of the capacitor 248 being connected to the outer conductor 234 and the other terminal of the capacitor 248 being connected to the terminal 202.

As has been explained above, the inner conductor 207 and the outer conductor 231 telescopically overlap a dista-nce equal to 1A wavelength of the frequency of operation of the oscillator 200. In addition, the probe 238, the inner conductor 240 and the choke 246 are also constructed to have a length equal to 1A wavelength of the frequency of operation of the' oscillator 200. In the operation of the coupler and filter structure 230, the 

